Generally, photolithography then etching is a well-known procedure in semiconductor process for forming fine patterns. Photoresist materials used in photolithography process should act as etching masks to protect the patterned material underneath from attack by etchants. However, in some cases where materials to be etched are too thick or having poor etching selectivity with respect to photoresist, unexpected defects or flaws may appear during the etching process and make it difficult to achieve expected pattern profiles.